The present invention relates to the upgrading of distillate fuels, and more particularly to a process for removing sulfur, nitrogen and aromatic compounds from distillate fuels using a multi-bed catalytic reactor.
When distillate fuels are produced from hydrocarbon feed, it is necessary to remove sulfur and nitrogen and to saturate the aromatics in order that the distillate fuel meets environmental standards and has a sufficiently high cetane number. When hydrocarbon feeds for producing distillate fuels are subjected to desulfurization, denitrogenation and dearomatization in a catalytic reactor, a significant temperature increase takes place across the reactor bed due to the exothermic heats of reaction. One known technique for compensating for this temperature rise in a multi-bed reactor is to use interbed gas and/or liquid quenching. In this type of process, the quenching fluid is introduced through distributors into a mixing device, known as a quench box, which is located between adjacent catalyst beds. The quench gas or liquid provides direct contact cooling of the reaction mixtures. When this technique is used, quench gas, which usually is recycle gas, is injected in a quantity sufficient to readjust the hydrogen partial pressure to the desired level. Quenching liquid, which usually is a recycle liquid, is then used to provide for the remaining cooling requirements.
There are several disadvantages to the above-mentioned direct contact cooling system. The use of recycle gas and/or liquid for direct contact cooling requires the use of relatively large compression equipment for supplying cooling gas. Furthermore, when cooling liquid is used, a larger catalyst volume may be required than would be needed if no liquid quench were used.